Palsa

Palsas are peat mounds with a permanently frozen peat and mineral soil core. They are a typical phenomenon in the polar and subpolar zone of discontinuous permafrost. One of their characteristics is having steep slopes that rise above the mire surface. This leads to the accumulation of large amounts of snow around them. The summits of the palsas are free of snow even in winter, because the wind carries the snow and deposits on the slopes and elsewhere on the flat mire surface. Palsas can be up to 150 m (490 ft) in diameter and can reach a height of 12 m (39 ft).^[1]

Permafrost is found on palsa mires only in the palsas themselves, and its formation is based on the physical properties of peat. Dry peat is a good insulator, but wet peat conducts heat better, and frozen peat is even better at conducting heat. This means that cold can penetrate deep into the peat layers, and that heat can easily flow from deeper wet layers in winter. Whereas the dry peat on the palsa surface insulates the frozen core and prevents it from thawing in the summer.^[1] This means that palsas can survive in a climate where the mean annual temperature is just below the freezing point.^[2]

A lithalsa is a palsa without peat cover. They exist in a smaller range than palsas, commonly occurring in oceanic climate regimes. However both palsas and lithalsas are relatively small compared to pingos, typically less than 3 m (9.8 ft).^[3]